Method and apparatus for sealing metal foil



July 26, 1960 J. G. D. MANWARING ETAL 2,946,168

J. G. D. MANWARING ETAI- July 246, 1960 ATUS FOR SEALING METAL FOIL 8Sheets-Sheet 2 Flled Oct. 8, 1957 July 26, 1960 J. G, D. MA'NWARlNG ETAL2,946,168

METHOD AND APPARATUS FOR SEALING METAL FOIL.

Filed OCT.. 8, 1957 8 Sheets-Sheet 25 Iawezzbads:

July 26, 1950 J. G. D. MANWARTNG ETAL 2,946,168

METHOD AND APPARATUS FOR SEALTNG METAL Fon.

Filed Oct. 8, 1957 8 Sheets-Sheet 4 EQ. //6b July 25, 1960 .1. G. D.MANwARaNG ETAL 2,946,168

METHOD AND APPARATUS FOR SEALING METAL FOIL Filed Oct. 8. 1957 8Sheets-Sheet 5 8/ l .i sii? l g FIG. 7. l l l l i 1 l (fi I r`\ "um Wugr L ava /Vl x1 7M 7m Il INVENTOR:

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rJuly 26, 1960 J. G. D. MANWARING ETAI- 2,946,168

METHOD AND APPARATUS FOR SEALING METAL FOIL Filed Oct. 8, 1957 8Sheets-Sheet 8 United States Patent Olice 2,946,168 Patented July 26,1960 METHOD AND APPARATUS FOR SEALING METAL FOIL Filed Oct. 8, 1957,Ser. No. 688,963

13 Claims. (Cl. 523-230) This invention relates to methods and apparatusfor use in the packaging of materials with which metal foil wrappers,such as aluminum foil, are utilized. More specifically, the invention isconcerned with the packaging of chocolate covered candies and variouscandy products, as well as other substances, in aluminum foil wrappedcontainers.

In a presently employed form of aluminum foil used in wrapping candyboxes in packaging machines, there is included the metal foil itselfover which is supported a thin coating of a wax-like adhesive materialcapable of melting in the presence of heat. The wax-like coating is inturn covered with a very thin layer of tissue or other fibrous sheetmaterial. In sealing together overlapping surfaces of such a foilproduct when wrapped around a container, a suflicient amount of heatmust be employed to melt or fuse the wax-like adhesive so that it willstrike through the tissue and become bonded against an adjacent wrappersurface.

ln attempting to satisfy the heat requirements by conventional forms ofheating equipment commonly employed in packaging machines and involvingthe use of heated applicator bars or similar instrumentalities, seriousdifficulties are encountered. In order to obtain an adequate heat flow,the package must be held in contact with the heating element over asubstantial period and along a contact area of considerable length. Thisarises from the fact that the aluminum acts as an insulating memberwhich tends to retard flow of heat inwardly to reach the wax-likeadhesive. It will be appreciated that an adequate heat flow to permeatethe aluminum foil will necessarily exert a considerable heating effectwithin the container, and this heat tends to become held within the foilWrapped container since the aluminum is equally effective in preventingheat dissipation. The net result is damage to the chocolate coveredcandy with its appearance being changed undesirably and its quality andsalability greatly impaired.

The speed of operation of conventional packaging machines utilizingother forms of wrapper material further complicates the problem, sincethe period required for heating the aluminum foil may require anappreciably longer period than is usually the case, and thus theeiiiciency of the packaging machine is lowered and output re tarded. Thetrate of packaging with conventional sealing equipment normally isusually not greater than fifty units per minute and this rate itself isless than that possible with well-known packaging machinery wheresealing is not a factor.

It is an object of the invent-ion tov deal with the problems indicatedabove and to devise methods and apparatus for applying heat to a metalfoil Wrapped container filled with chocolate covered candy, or otherproducts, in such a manner that an adequate sealing or bonding isaccomplished without undesirable heating of the container space orproducts held therewithin.

Another object of the inventionA is to provide a method and apparatusfor increasing the speed of sealing operations for metal foil wrappersand also to increase the practical rate of operation of packagingmachinery operation Vbeyond the standard output rate of machinesequipped with conventional sealing apparatus. Still another object ofthe invention is to combine with a method and apparatus of the classdescribed means for protecting the packaged material against excessiveheating, either from exposure to excessive heating conditions orextended heating periods.

With these objectives in mind, we have conceived of a procedure forapplying radio frequency heating to aluminum foil wrappers, as well asother metal foil wrapped packages, and we have devised a heatingapparatus for sealing metal foil containers in conjunction with anautomatic packaging operation at that point at which the metal foilwrapper has just been applied to the container. In one preferred aspectof our invention, a carefully controlled heat cycling apparatus iscaused to operate and to energize a heating coil as the foil Wrappedpackage moves into a sealing station in the packaging mach-ine.

An important feature of the apparatus of the invention is thecombination of a heating coil arranged in a special conformation, withthe heat cycling means, whereby exceedingly high frequency heat may beproduced for carefully limited intervals of time and along a sharplylocalized elongated zone of seal-ing with which folded ap portions of ametal foil wrapper may be held in register.

We find that this step of controlling high frequency heating may `berepeated at relatively high speed so that the continuous sealing orbonding operation may be satisfactorily synchronized with theconventional feeding and Wrapping cycle of a standard packaging machinewithout in any way impairing the efficiency or output of such machinesand, in fact, the equipment of the invention renders it possible toincrease the rate of output of such conventional machines.

We have also found that our method and apparatus for sealing may besuccessfully employed with various arrangements of flap portions andfolded sections of metal foil wrappers applied either -to chocolatecovered candies, other types of candies or products such as frozenfoods, butter, margarine and others. The foil or other metallic wrappermay be aluminum or any other suitable electrical conductor.

These and other objects and novel features will be more fully understoodand appreciated from the following description of a preferred embodimentof the invention selected for purposes of illustration and shown in theaccompanying drawings, in which:

Fig. 1 is a fragmentary perspective view showing portions of a standardtype of candy box packaging machine commonly employed in the trade;

Fig. 2 is another fragmentary perspective view of the machine shown inFig. 1 but viewed from an opposite corner thereof;

Fig. 3 is a detail cross-sectional view showing a porltion of themechanism of the packaging machine shown in Figs. 1 and 2 andparticularly illustrating a metal foil wrapped container in the positionin which it has been advanced to a sealing station for receiving highfrequency heat in accordance with the invention;

Fig. 4 is a cross-section taken on the line 4 4 of Fig. 3.

Q Fig. 5 is a perspective view showing a metal foil wrapped candy boxwith portions of the wrapper having been broken away to indicate moreclearly the line of sealing of the flap portions;

Fig. 6 is a diagrammatic view showing in detail the con- B formation ofthe work coil of the invention and its supporting base removed from thesealing station;

Fig. 7 is a plan View of transformer apparatus of the invention shownindependently of electrical circuitry and coolant connections;

Fig. 8 is a cross-section taken on the line 8-8 of Fig. 7;

Fig. 9 is another ,cross-section taken on the line 9-9 of Fig. 7;

Fig. 10 is a diagrammatic view further illustrating details of the heatcycling switch means of the invention and further illustrating theelectrical connection of this member with respect to other radiofrequency generating equipment;

Fig. 11 is a cross-section taken on the line 11-1111 of Fig. l;

Fig. 12 is a schematic view illustrating a cooling arrangement for aportion of the radio frequency generating equipment; Y

Fig. 13 is another schematic view illustrating a second coolingarrangement for anotherY part of the radio frequency generatingequipment; and

Fig. 14 is a current flow diagram employed in furnishing radio frequencycurrent in accordance with the invention to the sealing station.

Referring more in detail to the drawings, the apparatus shown includes,in general, a sealing unit which is adapted to be held momentarily incontact with a metal foil wrapped box of candy; electrical means forinducing a high frequency heating effect in the sealing unit, heatcycling cam switch means for controlling the operation of the highfrequency induction heating means; and mechanical feeding and wrappingmechanism for placing a metal foil wrapper in folded position about abox of candy and advancing the wrapped box into the sealing stationwhere it may overlie the sealing unit.

It will be understood that the sealing unit, together with the highfrequency induction means and the heat cycling switch apparatus,although shown in combination with one specic form of packaging machine,is not limited thereto, and the following description of the operationof the various parts is intended to be illustrative of application ofthe sealing unit and its related components to any other well-knownpackaging machine.

Referring more in detail'to Figs. 1 3, inclusive, arrow A denotesgenerally a packaging machine of the class in which a wrapping materialsuch as metal foil is fed from a feed roll mechanism B into one side ofthe machine with successive lengths being cut off to provide for acontinuous wrapping operation. At the left-hand end of the machine P, asviewd in Fig. 3, there is provided a conveyor 2 which is adapted toreceive and advance a box filled with candy in a direction from left toright. At an intermediate point in its forward travel, the filled box ofcandy moves into a conventional elevator device which raises the boxupwardly into engagement with a wrapper which becomes foldedtherearound. t

A portion of the conventional elevator and folding mechanism isl shownsomewhat diagrammatically in Figs. 3 and 4 wherein numeral 4 denotes alink-actuated elevator platform. The platform is shown in Fig. 3 in afully raised position and'supports a package P in a partly engagedposition with a metal foil wrapper W. A side conveyor C furnishes themetal foil wrapper which, as suggested in one position of the elevatorplatform noted in Fig. 4, is first caused to assume a position in whichit will be directly above the elevator in a lowered position. As apackage P2 comes onto the elevator platform and starts to rise, it willcome into contact with the wrapper and force it upwardly into positionsuch as that represented in Fig. 3 by package P.

Immediately after the package P reaches the position shown in Fig. 3, afolder 6Y folds one flap portion againstv opposite ap is folded intoplace. It will be understood that the machine operates in such a mannerthat one complete cycle of operation occurs to handle a single packagewith each rotation of the feed roll mechanism B from which foil isdelivered. Y

In the operation of conventional sealing mechanisms in well-knownpackaging machines, sealing may be accomplished along one side of thebox in one step and along opposite ends of the box in another step.Further details of packaging machine operations of the class referred toare described more fully in United States Patents 1,308,322, 1,329,236,1,330,354 and 1,283,342.

In accordance with the present invention, in one preferred form,inductionV heating is applied along that side of the box which is ofgreatest length where most difficulty has been experienced. Thereafter,the flaps at opposite ends of the box may be folded and sealed usingeither conventional heating alements or, if necessary to avoidoverheating, a further application of induction heating of theinvention. Y

The apparatus of the invention hereinafter described, therefore, hasbeen designed specifically for applying induction heating to overlappingportions of foil at a longer side of a box, it being understood thatthis heating operation may be repeated by substantially similar sealingmeans, ifdesired, in connection with sealing folded end aps or any otherfoil portions which are required to be secured.

Considering'in detail the sealing unit itself, an important factor isthe location of this sealing unit in a position'such that the box maypass immediately into contact therewith as soon as the aps are foldedinto overlapping relationship to one another. This arrangement has beenindicated diagrammatically by box P1 in Fig. 3. The sealing componentsinthe position noted occur between the elevator mechanism 4 and a secondconveyor member C2 shown at the right-handV side of Fig. 3.

A further important feature of the invention, therefore, is thecombination with the elevator mechanism and foil feeding components ofthe machine, of a sealing unit consisting of a supporting base 10 inwhich is embedded a special Work coil of the invention. By locating thesupporting base 10V with its upper surface lying in the plane of travelof the overlapping foil aps at the underside of the box, it is possibleto hold the overlapping portions snugly against one another at alltimes. At one point, the box may come to rest momentarily and the highspeed heating cycle of the invention may take place.

It is pointed `out that each heating cycle must take place during onecycle of operation of the metal foil feed roll mechanism and the precisepoints at which heating is initiated and terminated must be carefullytimed to allow a wrapped box to advance to the sealing station. At thesame time,Y the period of heating, because of its intensity, must besubstantially less than the time remaining before the roll mechanism Bhas completedv a single cycle of operation. This necessitatesinterrupting the operation of the work coil.

In meeting the needs of an adequate sealing of the metal foil flapsurfaces and yet avoiding excessively heating the box interior, we havefound-it necessary'to devise a special work coil conformation and toenergize this work coil by a unique transformer apparatus. Thetransformer. apparatus is mounted at one side of the packaging machine Aand is generally denoted by the arrow T in Fig. l. 'Heat cycle camswitch means for controlling the transformer apparatus T is combinedwitha suitable rotating part of the packaging machine A, preferably at anAopposite side thereof on a gear G (Fig, 1) associated with the metalfoil feed roll mechanism B.

In Figs. 5 and 6, we have illustrated the special coil conformationfound to satisfy the; particular sealing rcquirement of metal foilonboxes filled with chocolate covered candy when energized in aparticular manner, as hereinafter described.V In Fig. 5, we have shown abox P2 in an inverted position after it has been sealed and alsoindicating a bond of sealing L with a portion of the flap turned back.

As shown in Fig. 6, the work coil unit consists of the supporting base lcomprising a plastic such as fibre glass or other well-known dielectricmaterial in which is supported, preferably in an embedded state, acopper tubing element 16. This tubing element constitutes an electricalconductor which is reversely bent upon itself to form two adjacent coilswhich include outer coil sides 16a and 16b and inner `adjacent coilsides 16C, 16d and 16e. The inner adjacent coil sides 16e, 16d and 16eare carefully arranged in parallel coincident relationship in such amanner that they form inner current paths, as noted by the arrows, whichIare yadditive and which are capable of inducing an electromagneticfield of exceedingly high heating capabilities. This heating eld isconcentrated in -a narrow region which may be, for example, about 1A-inch wide and of a length consistent with the length of the box sidealong which sealing may take place las, for example, a length of 10-15inches.

An equally important factor in the concentration of heat thusaccomplished at the region 4of sealing noted is the functioning of theouter coil sides 16a and 1Gb. These two opposite sides providerelatively low heating since they `act as high heat dissipating paths.

It is pointed out that the ability of these outer coil sides 16a and 16bto dissipate heat can be greatly increased by widening the outer coilsides by means of flanges or similar structure which `tends to spreadthe current so that the difference between current at the outer coilsides and current at the inner adjacent coil sides becomes even morepronounced. Such a coil conformation, we find, is capable of producingan electromagnetic field when energized by a suitable high frequencycurrent -of an order of magnitude of from 500 kilocycles up to 1,00()-kilocycles In order to furnish the work coil with radio frequencycurrent of the frequency characteristics indicated, we have found thatit is necessary to employ a special transformer apparatus such as thatillustrated in Figs. 7, 8 and 9. This transformer apparatus comprisesessentially -a power supply and oscillator circuit in cornbination witha special tubular coil conformation constituting the primary andsecondary of a transformer device. In this special transformer coilconformation, there are employed coils of copper tubing which extendaway from a common center ground in the same direction of turning. Bymeans of this arrangement, the coils do not buck one another and astartling increase in coupling is accomplished at a relatively lowpotential so that insulation difficulties are at a minimum.

Numerals 200 and 200 indicate the two primary coil components whoseouter ends are connected by a conductor 200a. Numeral 400 indicates thesecondary disc element. This secondary disc element `400 consists of asplit annular body of short axial length and formed from a lowresistance material such as copper. The split ends ofthe annular body400 are provided with electrical output members 600 and 800. Thesemembers 600 and 800 have supported therethrough two sections of a highcurrent type Work coil member 16, which sections are made up of tubularcopper conductor portions whose ends are detachably connected bythreaded couplings to respective tubular extremities 700 and 700 of acoolant conduit 700. This conduit member is secured to the secondary 400and extends around its outer peripheral edge, as shown in Fig. 7. Acoolant, such as water, is supplied and removed through the connectingends 140 and 160 which are, in turn, connected to a suitable supplysource.

The primary coil components 200 and 200 may, for example consist of acontinuous length of copper tubing which is folded or bent over uponitself to provide a common junction or meeting point 210, as shown inFigs. 7 and 8. The two components are arranged in the form of two dished`or axially displaced spiralling coils so that the turns of each coilproject outwardly from either side of the secondary 400 `and extend inthe same direction to thus constitute mirror images of one another.

The two outer ends of the coils are connected to a source of R.F. powerof relatively high potential, such as 5,000 volts and each coil isgrounded at a common ground point through a ground strap attached to thejunction 210. Power is delivered to the coils `as R.-F. high voltageimpulses which are conducted along the surface of these tubular coils. Acoolant, such as water, is circulated through the coils from a suitablesupply source which may be taken from the same source of supply forcooling the secondary member. Each turn of the primary coils is coveredwith a solid type insulation material which provides limited insulationwith optimum induction effects and, in addition, each of the primaryturns are supported upon spacing wedges 220 located at several pointsaround the two opposite surfaces of the secondary disc 400, as bestshown in Figs. 8 and 9. These wedging members thus control the degree ofaxial displacement of the respective primary coils from adjacentsecondary surfaces and thus provide a convenient means of decreasing thespacing of the primary coils with decreasing voltage potential whichranges from a maximum at the outer peripheral edges of the secondary toa minimum at the inner peripheral edges thereof. The water coolingsystem for the secondary is Ifurther shown in Fig. 12. Similarly, thecooling system -for the primary is shown in Fig. 13. Numerals 201 and 2Mare rubber water coils and 263 is a tank condenser with a drain 204.

The structure described is characterized by several important features,all of which combine to produce relatively heavy current carryingcapacity with small loss and to cooperate with the special design of thecoil 16. The principal feature to be noted is that the secondary in theparticular position in which it is arranged relative to the primary isadapted to produce a very strong coupling of magnetic flux. This isbecause the secondary occurs in the center of the primary in the rstinstance, and in the second instance, the arrangement is such that muchless voltage insulation is required to `avoid trouble. By bringing theprimary very close to the secondary, as is achieved by having ltwo setsof spiralling coils at either side of the secondary, a maximum ofcoupling is achieved at all points with the adequate amount of voltageinsulation being provided for. Moreover, it is pointed out that there isa voltage condition which is at its maximum in entering the primarywhere the spacing of the dish spiraling coils is greatest, and thevoltage tapers to a minimum` where the spacing of the two sets of coilsis. at a minimum or nearly zero magnitude.

In Fig. 14, we have illustrated a current flow diagram for thetransformer apparatus T. Also included are electrical power supplymeans, an oscillator circuit, together with the primary coil andsecondary parts of Figs. 7, 8 and 9 with the latter member including thework coil 16 which, las shown in Fig. 5, is embedded in the supportingbase 10 of the sealing unit.

Voltage from a suitable supply line is stepped up to a desired voltage,such as 3500 volts. Rectifier tubes 5' change the voltage to pulsatingD.C. voltage. Current from the power supply plate transformer 7' flowsto oscillator tube 13 passing through a tank coil 1-6' and then to theradio frequency transformer primary 200 toground.

The rectified voltage is applied between the plate of the oscillatortube 13 and the filament of this oscillator tube providing a voltagewhich controls the ow of electrons `from the tube `filament to theplate. The flow of electrons through the tube is partially controlled bythe grid bias voltage which is negative at the grid with respect to thefilament and is obtained by the flow of grid current through the gridresistor.

As soon as the voltage is applied to the oscillator tube 13', currentflow starts oscillations in the tank circuit,

7 including the tank coil 264)` and coil 16'. The rate or frequency atwhich the current flows back and forth in the tank circuit is determinedby the inductance of the tank coils 200 and 16 and the capacitance i5. Ahigh radio frequency voltage is developed across the tank coil due ytothe high current owing in the tank circuit. This high radio frequencycurrent flowing in the primary of the transformer induces current in thesecondary 461B of the transformer due to the mutual inductance of thetwo windings, as above described. When an electrical conductingmaterialis placed in the electromagnetic field formed by the radiofrequency current owing in the work coil 16, current is induced into thematerial. Since the current is reversing at a high rate, friction iscreated between the molecules of the material, thereby developing heat.

In Fig. 10, we have illustrated the heat cycling cam switch apparatuswhich we combine with the circuit of Fig. 14 to control the operation ofthe work coil. As shown in Fig. l0, a shaft rotation switch 59 of someconventional nature, such as the Zero Speed Control manufactured by TheWinter-burn Manufacturing Company of Putnam, Connecticut, is fixed to ashaft 52 which -is located at the upper side of the packaging machine A.This shaft is Vgeared to drive which rotates the feed roll mechanism Band is indicated in Figs. l and 2. Rotation of shaft 52 holds thecontacts of switch Si? in a closed position and, as soon as the shaft i)stops turning, the circuit is opened in the conventional manner.

In series with the shaft switch Sit is a second cam activatedmicroswitch 51 of the invention which is connected into `one side of theline running to a grid of the rectifier tube 5 in Fig. 14. Thismicroswitch is mounted above the shaft of roll B in a position such thata spring con- -trol arm 54 normally rides on a cam 56 and maintains thecircuit in a closed state. The cam S6 is supported on a suitable shaftof feed roll mechanism B, as shown in Fig. 2 and, as indicated in Fig.ll, is madeup of two cam segments 56a and 56b secured in spaced relationon the shaft by set screws as 56e and 56d. By varying the position ofthe cams relative to one another, a dwell 56e is provided and this dwellmay be varied through any desired larc to control the period in whichthe switch 51 may remain closed and, in particular, a time interval oflimited duration for heating is accomplished. A cam adjustment whichwill provide for the switch being closed for a 320 interval is suitablefor properly limiting the heating period of coil 16.

With the arrangement described, a desirable protection againstundesirable heating is realized either from the machine stopping or forany other reason. At the same time, a very precise cut-off of intenseheating may be realized.

By means of the combination of special work coil shape and specialtransformer apparatus for energizing this work coil shape, an intensenarrow band of heating is accomplished in a carefully limited timeinterval. Highly intensied heat is developed by fthe particularelectro-V magnetic eld induced in a metal foil surface which ismomentary held above the work coil 16. As a result, we nd that we areenabled to melt or fuse the wax-like adhesive on the metal foil, earlierdescribed, in such a rapid manner that theY melted adhesive instantlystrikes through the tissue backing of the aluminum foil and a part ofthis fused or melted adhesive becomes transferred onto an adjacentymetal foil surface of an underlying flap.

the outer exposed surfaces of the metalV foil. rIhis is irnportant'sincethe metal foil is found .to take a ne finish of printed material greatlyenhancing the value of the foil as a wrapping material. By controllingour heating operation in the manner described, there is no change inthis printed material on exposed surfaces ofthe wrapper.

Still a further advantage realized in this rapid high intensity heatingstep is an increase in the capacity of the machine as compared with itscapacity when using conventional heating means. We find that we mayutilize our induction heating method and apparatus to step up the rateof operation, for example, from 50 sealing operations per minute up toto 1GO sealing operations per minute `or higher. This is a substantialimprovement in package machine operations using metal foil. The heatcycling cam switch apparatus, in addition to performing the describedcontrol of the heating period, affords another desirable advantageV inthat exceedingly long life may be realized from the apparatus describedand the possibility of breakdown or early wearing outof moreconventional parts, such asY time control relay mechanisms, is avoided.Finally, in conjunction with all of the above recited advantages, thereis realized a simplification of installation of heating 4means in anystandard type of packaging machine and a much greater degree ofexibility in the use of such machines is present.

it is contemplated Vthat the method and apparatus of the invention maybe modified in various respects wherein the basic combination of specialwork coil shape and special Vtransformer energizing means may be adaptedto varying types of packaging machinery and to meet the requirements ofvarying demands in shapes and sizes of metal foil wrapped containers fora wide range of products.V Although a single band of sealing has beendisclosed with the special work coil shape of the invention, it will beappreciated that two or more bands of sealing or various otherarrangements of bonding overlapping surfaces may be accomplished by theinvention.

Therefore, while we have shown and disclosed preferred embodiments ofthe invention, it will be understood-that changes and modifications maybe resorted to within the scope of the appended claims.

Having thus described our invention, what we claim is:

I. An induction heating apparatus -for sealing metal foil, saidapparatus comprising a sealing unit consisting of a supporting base anda work coil embedded in theV supporting base, said supporting basepresenting an upper at surface for receiving a foil wrapped package withoverlapping foil portions occurring at the underside of the package,said embedded work coil means including two elongated inner coil sidesoccurring in parallel spaced relation -to one another in close proximityto the surface vof the supporting base thereby to form inner currentpaths of high intensity and said coil further including two outer coilsides which provide high heat dissipating paths and said inner coilsides being spaced to define a narrow elongated zone of heating whichsubstantially corresponds to the area along which the said foil portionsoverlap and electrical transformer means for energizing said work coil.

2. A structure according to claim l in which the work coil consists of acontinuous length of electrically conductive tubing.

3. An apparatus according to claim 1 including switch means forcontrolling the Voperation of the transformer, said switch meansincluding adjustable cam segment mechanism for controlling the timeinterval during which the transformer remains energized.

4. ln a packaging machine for applying `a foil wrapper to a container,means for advancing and supporting a container in a position to receivethe wrapping material, means for folding the wrapping material :aboutthe container to provide over-lapping foil portions, a heat seal unitfor temporarily supporting the container while the overlapping wrapperportions are held in contact with one another at the underside of thecontainer, said sealing unit including a dielectric base having a atsupporting surface, a work coil embedded in the dielectric base 1n closeproximity to the flat supporting surface, said work coil including innercoil sides which dene current paths of high intensity yand outer coilsides which constitute high heat dissipating paths.

5. An apparatus according to claim 4 in which the inner coil sides arearranged in spaced relation to define a zone of heating whichcorresponds approximately to the area included by the overlapping foilportions.

6. An apparatus according to claim 4 including transformer means forenergizing said Work coil 4and switch means for controlling operation ofsaid transformer, said switch means consisting of a cam segmentmechanism and micro switch which opens and lcloses a circuit through thetransformer during each wrapping cycle of the packaging machine and saidcam segment mechanism being adapted to vary the period during which thetransformer is energized during each machine cycle.

7. In -a packaging machine for applying a foil wrapper to a container,means for 'advancing and supporting a container in a position to receivethe wrapping material, means for folding the wrapping material about thecontainer to provide overlapping foil portions, a heat seal unit fortemporarily supporting the container While the overlapping wrapperportions are held in contact with Ione another at the underside of thecontainer, said sealing unit including a dielectric base having a flatsupporting surface, a work coil embedded in the dielectric base in closeproximity to the flat supporting surface, said work coil including innercoil sides which deline current paths of high intensity and outer coilsides which constitute high heat dissipating paths, transformer meansfor energizing said coil, electrical switch means for controlling theoperation of the transformer, said switch means including means forinterrupting operation of the transformer whenever the packaging machinecornes to rest and a second micro switch mechanism for providing apredetermined dwell during which period the transformer is held inoperative position while the packaging machine is running.

8. In a packaging machine, means for feeding a container forwardly,means for applying 1a metal lfoil wrapper about the container with itsedges in overlapping relationship to one another, mechanism foradvancing the foil wrapped container into a sealing station, a containersupporting member located in the sealing station and having a Work coilembedded therein, said Work coil being arranged to define a heating`area which extends in a relatively narrow zone coinciding lwith theoverlapping portions of the metal foil wrapper, transformer apparatusfor furnishing radio -frequency ycurrent to said Work coil, and meansfor interrupting the ilow of current from the transformer to the workcoil periodically, said means for interrupting the flow of currentcomprising a switch which is normally closed when the machine isapplying the metal foil wrapper to the said container and which isopened lwhen the packaging machine is at rest, and ya second camactuated switch arranged to open a ycircuit from the transformerapparatus to the work coil after a time interval has elapsed of aduration less than the time interval required for the machine to makeone cycle of operation.

9. A structure according to claim 1 in which the transformer deviceincludes a secondary electrical conductor, a primary electricalconductor consisting of two spacedapart coils supported at oppositesides of the secondary electrical conductor, Said coils being joinedtogether at a common central ground point and having their outer endsconnected to a common terminal, each of said coils having itsconstituent turns originating in close proximity to the secondaryelectrical conductor and extending away from the common ground point inthe same direction, whereby high voltage impulses applied to the primarywill produce flux paths for the two coils, which flux paths combine inseries and are additive.

ll0. An apparatus for sealing metal foil comprising a supporting basefor receiving an enclosure body which presents overlapping metal foilportions, means in said supporting base for selectively applying heatwhich is localized on adjacent surfaces Iof the said overlapping metalfoil portion to bond the surfaces without appreciable change intemperature within the enclosure body, said means for applying heatincluding an electrical transformer device for producing radio frequencycurrent and work coil means mounted in the supporting base for receivingsaid radio frequency current and producing a lacalized electromagneticiield of high voltage characteristics, said -work coil consisting of atubular conductor consisting of two loop portions, said loop portionsbeing arranged one -beside another to define two opposite outer loopsides land two inner adjacent loop sides, said inner loop sidesoccurring in substantially parallel relationship to coincide with oneanother and to form inner current paths which are additive and which arecapable of inducing a relatively high heating effect, and said oppositeouter loop sides providing relatively low heating, high heat dissipatingpaths.

l1. In an induction heating device for sealing metal foil surfaces toone another, electrical transformer means for producing radio frequencycurrent and work coil means constructed and arranged to receive radiofrequency current from said electrical transformer means, said work coilmeans comprising a tubular conductor consisting of two loop portions,said loop portions being arranged to fdene two opposite outer loop sidesand two inner adjacent loop sides occurring 'm substantially paralleloverlapping relationship to coincide with one another and to formadditive inner current paths -for inducing a relatively high heatingeifect and said opposite outer loop portions providing Irelatively lowheating current paths.

12. A structure according to claim 4 in which the transformer apparatuscomprises in combination a secondary electrical conductor, a primaryelectrical conductor consisting of two spaced-apart coils supported atopposite sides of the secondary electrical conductor, said coils beingjoined together at a common central ground point and having their outer`ends connected to a common terminal, each of said coils having itsconstituent turns originating in close proximity to the secondaryelectrical conductor and extending away from the common ground point inthe same direction, whereby high voltage impulses Lapplied to theprimary will produce flux paths for the two coils, which ux pathscombine in series and are additive.

13. A structure according to claim 8 in which the cam actuated switchincludes an adjustable cam body which is adapted to make one revolutionduring each cycle of operation of the packaging machine, said adjustablecam consisting of two cam segments removably secured together, each ofsaid segments presenting recessed dwell surfaces which may vbe variableyspaced with respect to one another.

References Cited in the tile of this patent UNITED STATES PATENTS2,195,222 Neumair Mar. 26, 1940 2,342,532 Doelker Feb. 22, 19442,446,414 Farrell et al Aug. 3, 1948 2,676,444 Gaubert Apr. 27, 19542,723,517 Mittelmann Nov. 15, 1955 2,818,483 Blume Dec. 31, 1957

